The present invention relates generally to anchoring apparatus utilized in subterranean wells and, in an embodiment described herein, more particularly provides a packer for use in extreme service conditions.
In a typical packer having a single slip, which may consist of a single slip member or multiple circumferentially distributed slip segments, forces applied to the packer are necessarily resisted by the same slip. Thus, when a downwardly directed tubing load and a downwardly directed differential pressure are applied to the packer, the single slip must resist both by its gripping engagement with a tubular structure (such as casing, tubing, other equipment, etc.) in which it is set. In extreme service conditions, the slip may need to be radially outwardly forced into contact with the tubular structure, in order to resist the forces applied to the packer, with enough force to cause damage to the tubular structure, the packer, or both.
If the gripping surface area on the slip is increased in an attempt to increase the gripping engagement between the slip and the tubular structure, it has been found that it is more difficult for the slip to initially bite into the tubular structure. This is due to the fact that more of the slip is required to deform more of the tubular structure. Consequently, more radially outwardly directed force must be applied to the slip, thereby causing damage to the tubular structure.
It would be advantageous to be able to use multiple axially spaced apart slips on an anchoring device, in order to distribute forces applied to the device among the slips. In addition, it would be advantageous for each of the multiple slips to be dual slips, so that each of the slips could resist forces applied thereto in both axial directions. Unfortunately, the use of multiple axially spaced apart slips presents additional problems, particularly when the slips are dual slips.
For example, it may be difficult to retrieve the anchoring device after the slips have been grippingly engaged with the tubular structure. This is due to the fact that slips generally have inclined teeth, serrations, etc. formed thereon which, when axially opposed with other slips, resist disengagement from the tubular structure.
As another example, mechanisms to extend and then retract multiple slips may be prohibitively complex, and therefore unreliable, uneconomical and/or too delicate for use in extreme service conditions. Thus, an extreme service anchoring apparatus utilizing multiple axially spaced apart slips should include appropriately robust, economical and reliable mechanisms for extending the slips and, where the apparatus is to be made retrievable, should include a retracting mechanism with similar qualities.
From the foregoing, it can be seen that it would be quite desirable to provide an anchoring apparatus which minimizes damage to a tubular structure in which it is set. The apparatus would make advantageous use of multiple slips and include an appropriate mechanism for extending the slips and, where the apparatus is to be retrievable, include an appropriate mechanism for retracting the slips. It is accordingly an object of the present invention to provide such apparatus and associated methods of anchoring and releasing the apparatus within the tubular structure.